AJAX is used for allowing the client side of an application to communicate with the server side of the application. Before AJAX, there was no way for the client side of a web application to communicate directly with the server. Instead, we would have to use page loads. With AJAX, the client and server can communicate freely with one another.
Instead of going to a login page, and then navigating back to the page you originally wanted, with AJAX, we can type in their user name and password directly into the original page. From there AJAX will send a request to the server to log them in. The server let’s the page know they’ve been logged in, and the page we are on can update as needed.
Google was one of the first major companies to start using AJAX, and Google’s search suggestion tool was one of the first ways they used it, and one of the first auto-complete tools made. When typing into the Google search bar, it starts to use AJAX to get common results from the database on each keystroke. Auto-Complete is great for forms where you have a lot of possible inputs, and making a select drop down would be too long and cumbersome.
Social bookmarking sites let the users decide the main content of the site by voting on content that the users like. They use AJAX to handle all of the voting, so that the users are able to voice their opinions on a number of stories quickly and easily.
One of the things that made Twitter so popular was their simple and easy-to-use interface. When someone makes a ‘tweet’, it is instantly added to their feed, and everything is updated. Recently, Twitter has started using AJAX with their ‘trending topics’ pages. Every few seconds, the page lets the user know that more tweets have been made about the subject, giving them up-to-the-second updates.
Forms have always tricky to work with, but AJAX can make them a lot better for the users. AJAX can be used in a variety of ways, from the auto complete mentioned above, to validation and submission as well. Some sites use AJAX to check if a form meets certain requirements, such as password strength, or if something is a valid email or URL.
Creating a clean, slick user interface is a very popular use of AJAX. It allows users to accomplish more on a single page. The benefits of this are twofold: First, it makes using the web application quicker and easier for the user; Secondly, it cuts down on the number of requests you have to make to the server, which cuts down on bandwidth and load times. A free file upload service called Drop.io uses this well. Google has also really pushed the envelope of what is possible with AJAX by making desktop-like applications like Google Docs and Google Maps.
Pop-up blockers are very common place these days, and for a good reason: pop-ups are annoying. Using light boxes, which are pop-ups inside the browser window, the pop-up blocker can’t stop it, and they aren’t quite as irritating to the user. Some people use them for advertising.